ON THE NONLINEARITY OF SILICON DETECTORS AND THE ENERGY CALIBRATION IN RBS

The response of silicon surface barrier and passivated ion implanted d etectors to He-4 ions of energies up to 5.5 MeV was studied. The detec tor function was found to be nonlinear with remarkable effects on RBS spectra and their interpretation. The nonlinearity affects the relativ e energies in a spectrum and needs correction, if e.g. thin interface reaction or segregation zones have to be identified. Also, if an absol ute energy calibration is performed with an additional alpha-signal fr om a radioactive source, the nonlinearity of the detector leads to a r emarkable error. The measured nonlinearity is well described by the en ergy loss of the detected particle in the detector window and by the d ependence of the electron-hole pair creation energy on the stopping po wer in the detector material, as predicted by the model of Lennard et al. [Nucl. Instr. and Meth. A 248 (1986) 454]. On the basis of this mo del, parametrization of the detector response and linearization of the spectra are possible. The reliability of RBS data interpretation is s ignificantly improved by such a linearization.